OB: Practice phase concepts:
cooling and heating curves,
phase diagrams, pressure
conversions, table H problems.
Take out NEW reference tables.
Recycle the old ones NOW.
Draw the Cooling curve for cobalt. On the same graph, draw the heating curve for
cadmium. Titles, axis labels and scales, be big.
3200
2400
Temp
Kelvin
1600
800
Energy added (or removed) at constant rate over time
Draw the heating curve for cobalt. On the same graph, draw the cooling curve for
cadmium. Titles, axis labels and scales, be big.
3200
Cadmium
BP: 1040 K
FP: 594 K
2400
Temp
Kelvin
1600
Cobalt
BP: 3200 K
FP: 1768 K
800
Energy added (or removed) at constant rate over time
Why are the flat lines different lengths on every heating curve (and every cooling curve)?
BC represents the melting
of ice. It takes for water,
334 Joules of energy to
melt one gram of ice from
solid to liquid without
increasing the temperature.
It’s called the heat of fusion
For water: HF = 334 J/gram
DE represents the boiling of
water into steam. It takes
for water, 2260 Joules of
energy to vaporize one gram
of water to steam without
increasing the temperature.
It’s called the heat of
vaporization
For water: HV= 2260 J/gram
The phase change from liquid to
gas is MUCH more energetic than
melting solid to liquid. For
water, it’s nearly 7X more!
A phase diagram shows one substance’s range of phases through temperature and pressures.
Below is the phase diagram for water.
Special Points on this
graph:
Tm: normal melting point
Tb: normal boiling point
TP: triple point
CP: critical point
Imagine you have two beakers of liquid, one has 500. mL ethanol alcohol and the other
has 500. mL of propanone. They are sitting on the desk in front of you. Put a cork into
each top.
AIR PRESSURE
101.3 kPa
Start pressure
inside flasks
the same
Warm up the
room to 25⁰C
What is
pressure
inside each
flask?
Imagine you have two beakers of liquid, one has 500. mL ethanol alcohol and the other
has 500. mL of propanone. They are sitting on the desk in front of you. Put a cork into
each top.
AIR PRESSURE
101.3 kPa
Start pressure
inside flasks
the same
25⁰C
Vapor Pressure ethanol
@ 25⁰C is about
8 kPa
Vapor pressure propanone
@ 25⁰C is about
31 kPa
What if we heat it up to 65⁰C next???
Imagine you have two beakers of liquid, one has 500. mL ethanol alcohol and the other
has 500. mL of propanone. They are sitting on the desk in front of you. Put a cork into
each top.
AIR PRESSURE
101.3 kPa
Start pressure
inside flasks
the same
65⁰C
Vapor Pressure ethanol
@ 65⁰C is about
60 kPa
Vapor pressure propanone
@ 65⁰C is about
135 kPa
KABOOM!
Properties of SOLIDS, LIQUIDS, and GASES Compared
SOLIDS
Particles are strongly attracted to each other, other than some vibration there is
nearly no movement of the atoms or molecules, they have a rigid or lattice
arrangement of the particles, they keep their shapes and volumes, they do not
take the shape of their containers. Solids cannot be compressed very much
because the particles are very close together.
Because of this most solids have a high density compared to their liquids or
gases. When energy or heat is added, the particles will vibrate more, which often
makes solids expand when heated. Particles in solids have the lowest kinetic
energy. Give solids enough energy (at the proper pressure) and they will vibrate
so much that they break apart and turn into ....
LIQUIDS
Particles have some attraction to each other but not enough to make
them stuck. Liquids flow over themselves, the particles are in
constant random motion. Liquids do not have a definite shape which
means they take the shape of the container you put them in.
If you spill liquids, the force of gravity spreads them out quite well.
The hotter liquids get when you add energy, the faster the particles
move, and liquids too expand slightly when heated. Liquids are dense
as well, but usually not as dense as solids are. Heat a liquid enough,
the particles move so much that they turn into...
GASES
There is virtually no attractive or repulsive force between the
particles. The particles move in straight lines and very fast. They
collide with other particles all of the time. These collisions will cause
gas (or air) pressure. Gases take the shape of the container that you
put them in. Any amount of a gas will fill any container that you put
it in.
The collisions are considered to be elastic, meaning there is no loss
of kinetic energy due to the collisions. Heated gases make the
particles move faster and have more collisions, causing expansion if
possible, or greater pressures if contained in a definite volume. Gas
Particles have the highest kinetic energy. Gases have very low
density.
Gas Pressure is measured with different pressure units, all on table A. Let’s add mm Hg
now to the new tables.
1.0 atm = 760. mm Hg = 101.3 kPa = 14.7 psi
Today’s pressure is exactly 1.14 atm.
Convert that to mm Hg, and kPa right now…
This slide left
intentionally
blank, you
know why…
1.14 atm X
1
760. Mm Hg = 866 mm Hg
1.0 atm
1.14 atm X 101.3 kPa
1
1.0 atm
= 115 kPa
(3 SF)
(3 SF)
1st
At any one temperature, say 65°C,
ethanonic acid has the lowest
vapor pressure, propanone the
highest. WHY???
Each liquid, these 4 included,
at any one temperature will
evaporate to a certain
degree.
How much this happens is
connected first to the
temperature, and then, to
how strong the intermolecular attractions the
molecules have for each
other.
At 65°C
Propanone has the lowest
intermolecular attraction
and therefore the highest
vapor pressure.
Ethanoic acid has strong
intermolecular attraction,
so low vapor pressure.
Put a small note onto your reference tables if you want to now.
Propanone has the highest vapor pressure
of these four, at any temperature,
because it has the weakest intermolecular
attractions for itself.
Ethanoic acid has the
lowest vapor pressure
of these four, at any
temp. because it has
the strongest
intermolecular
attractions for itself.
Heating curve for an unknown substance
BP
in
K
FP
Energy being added at a constant rate over time.
Heating curve for an unknown substance
D
BP
E
From BC there is no change in temperature.
in
K
FP
PE
From DE there is no change in temperature.
Ergo: Kinetic Energy is steady.
B
PE
Potential Energy must increase there.
C
Energy being added at a constant rate over time.
Heating curve for an unknown substance
D
BP
E
in
Temp
K
KE
FP
From CD there is an increase in temperature.
That means Kinetic Energy Increases too
If kinetic energy is changing, Potential
energy is steady (doin’ nutin’)
B
C
Energy being added at a constant rate over time.
Kinetic Energy & Temperature are the same thing, sort of.
The greater the KE, the greater the temp.
Lower temp = lower KE
Temp + Kinetic energy
are like Michael Jackson’s hand & his glove.
What ever one does, so does the other.
The other energy, Potential Energy,
is used when there is no change in
the kinetic energy. It’s for those phase change times.
If kinetic energy (temp) is changing, potential energy is steady.
In a phase change kinetic energy is steady (so is temp),
then the PE is going up in a heating curve, or
the PE is going down in a cooling curve.
Over break, make sure you read through
all the diaries that you missed.
Complete all through the phases diary.
In January we begin thermochemistry.
It’s a bunch of math, fun labs, and you’ll
want to get an amazing tattoo of
the formula.
Q = mC∆T